Semiconductor devices are commonly found in modern electronic products. Semiconductor devices vary in the number and density of electrical components. Discrete semiconductor devices generally contain one type of electrical component, e.g., light emitting diode (LED), small signal transistor, resistor, capacitor, inductor, and power metal oxide semiconductor field effect transistor (MOSFET). Integrated semiconductor devices typically contain hundreds to millions of electrical components. Examples of integrated semiconductor devices include microcontrollers, microprocessors, charged-coupled devices (CCDs), solar cells, and digital micro-mirror devices (DMDs).
Semiconductor devices perform a wide range of functions such as signal processing, high-speed calculations, transmitting and receiving electromagnetic signals, controlling electronic devices, transforming sunlight to electricity, and creating visual projections for television displays. Semiconductor devices are found in the fields of entertainment, communications, power conversion, networks, computers, and consumer products. Semiconductor devices are also found in military applications, aviation, automotive, industrial controllers, and office equipment.
Semiconductor devices exploit the electrical properties of semiconductor materials. The atomic structure of semiconductor material allows its electrical conductivity to be manipulated by the application of an electric field or base current or through the process of doping. Doping introduces impurities into the semiconductor material to manipulate and control the conductivity of the semiconductor device.
A semiconductor device contains active and passive electrical structures. Active structures, including bipolar and field effect transistors, control the flow of electrical current. By varying levels of doping and application of an electric field or base current, the transistor either promotes or restricts the flow of electrical current. Passive structures, including resistors, capacitors, and inductors, create a relationship between voltage and current necessary to perform a variety of electrical functions. The passive and active structures are electrically connected to form circuits, which enable the semiconductor device to perform high-speed calculations and other useful functions.
Semiconductor devices are generally manufactured using two complex manufacturing processes, i.e., front-end manufacturing, and back-end manufacturing, each involving potentially hundreds of steps. Front-end manufacturing involves the formation of a plurality of die on the surface of a semiconductor wafer. Each die is typically identical and contains circuits formed by electrically connecting active and passive components. Back-end manufacturing involves singulating individual die from the finished wafer and packaging the die to provide structural support and environmental isolation.
The package has external metal contacts for transferring electrical signals into and out of the die. The die has a number of bond pads, which are connected to the external contacts of the package by wire bonds. Wire bonding provides an electrical interconnect between the active surface of the die and bond sites on a leadframe or bond fingers on the substrate, which in turn provide connectivity to other circuitry external to the semiconductor package.
One goal of semiconductor manufacturing is to produce smaller semiconductor devices. Smaller devices typically consume less power, have higher performance, and can be produced more efficiently. In addition, smaller semiconductor devices have a smaller footprint, which is desirable for smaller end products. A smaller die size may be achieved by improvements in the front-end process resulting in die with smaller, higher density active and passive components. Back-end processes may result in semiconductor device packages with a smaller footprint by improvements in electrical interconnection and packaging materials. Numerous package approaches have made use of multiple integrated circuit die or package-in-package (PiP) structures. Other approaches use package level stacking or package-on-package (PoP) arrangements. Both approaches involve the stacking of two or more devices or packages within a package.
FIG. 1 illustrates one known PiP structure. Semiconductor die 12 is attached to substrate 14 with die attach adhesive 16. Bond wires 18 make electrical contact between bond pads on semiconductor die 12 and bumps 20 to transfer electrical signals into and out of the package. Similarly, semiconductor die 22 is attached to substrate 24 with die attach adhesive 26. Bond wires 28 make electrical contact between bond pads on semiconductor die 22 and bumps 20 to transfer electrical signals into and out of the package. An encapsulant 32 seals semiconductor die 22 to form internal stacking module (ISM) 34. A dummy spacer 30 separates semiconductor die 12 and ISM 34, and provides structural support for the package. Adhesive 38 secures dummy spacer 30 to semiconductor die 12 and ISM 34. FIG. 2 shows a top view of an ISM with package test pads 42 and bond finger pads 44.
There is an ever-increasing demand for semiconductor devices having more capability. The semiconductor package must be able to accommodate more semiconductor devices, i.e., greater device packing density, within the package. The aforedescribed dummy spacer requires significant space and places demands on the headroom of the package. The dummy spacer reduces the space available for semiconductor device and thereby decreases the packing density of the PiP structure.